A cellular telephone and its user fee are too expensive to be sufficiently supplied to everyone. A radio pager is considerably cheaper than the cellular telephone and is capable of easily informing people where and why the user called. Hence, radio pagers are increasingly used instead of the cellular telephone.
As illustrated in FIG. 1, a conventional radio pager includes an antenna and receiver 1 for receiving the call number data transmitted from the central office, an identification read only memory (ID-ROM) 3 for storing an identification ID of the pager, and a comparator 2 for comparing the data received by the receiver 1 with the identification data ID of the pager stored in the ID-ROM 3. The comparator 2 re-transmits the result to the receiver 2 and controller 13.
A memory 6 stores the received call number data, and a first driving unit 9 drives a speaker 11 to generate sound if the ID stored in the ID-ROM 3 and the received call number are the same. A second driving unit 10 turns on a light emitting diode (LED) 12. A displaying unit 8 displays the call number data, the pager's conditions, and time from the buffer 7, which are stored in the memory 6. A timer 5 displays the time and an input key 4 is provided to input time or simple data, such as a telephone number. A control unit 13 controls the operation of each pager component.
The data received from the central office includes, as illustrated in FIG. 2, an address word A and a message word M. The address word A comprises a sequence of one flag bit 1, an address bit 2, a function bit 3, and a check bit 4. In a case of a first message word after an address bit, the message word comprises a sequence of one flag bit 1, a selection code 5, a pure message 6 and a check bit 4. The pure message word 6 is repeated twice after an address word A.
As shown, the conventional radio pager is configured to receive only the call number, although the pager has enough capacity to supply several types of data. As a result, the usage of the conventional pager is very limited.